Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
  • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
  • H04N1/4055—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern
  • H04N1/4056—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern the pattern varying in one dimension only, e.g. dash length, pulse width modulation [PWM]
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G15/00—Apparatus for electrographic processes using a charge pattern
  • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
  • G03G15/04027—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material and forming half-tone image
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G15/00—Apparatus for electrographic processes using a charge pattern
  • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
  • G03G15/04036—Details of illuminating systems, e.g. lamps, reflectors
  • G03G15/04045—Details of illuminating systems, e.g. lamps, reflectors for exposing image information provided otherwise than by directly projecting the original image onto the photoconductive recording material, e.g. digital copiers
  • G03G15/04054—Details of illuminating systems, e.g. lamps, reflectors for exposing image information provided otherwise than by directly projecting the original image onto the photoconductive recording material, e.g. digital copiers by LED arrays
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G15/00—Apparatus for electrographic processes using a charge pattern
  • G03G15/22—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20
  • G03G15/32—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the charge pattern is formed dotwise, e.g. by a thermal head
  • G03G15/326—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the charge pattern is formed dotwise, e.g. by a thermal head by application of light, e.g. using a LED array
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
  • G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
  • G06K15/12—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers
  • G06K15/1238—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point
  • G06K15/1242—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point on one main scanning line
  • G06K15/1247—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point on one main scanning line using an array of light sources, e.g. a linear array
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/387—Composing, repositioning or otherwise geometrically modifying originals
  • H04N1/3871—Composing, repositioning or otherwise geometrically modifying originals the composed originals being of different kinds, e.g. low- and high-resolution originals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
  • H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
  • H04N1/40031—Circuits exciting or modulating particular heads for reproducing continuous tone value scales for a plurality of reproducing elements simultaneously
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
  • H04N1/401—Compensating positionally unequal response of the pick-up or reproducing head

Definitions

• the present invention relates to reproduction apparatus comprising non-impact printing apparatus for recording on a moving photoreceptor and a printhead for use therewith.
• U.S. Patent No. 4,521,814 printing apparatus which comprises a pair of individually addressable and energizable point-like radiation sources, such as lasers, arranged for exposing points upon a photoreceptor during movement thereof relative to the radiation sources.
• Driver circuits are provided for simultaneously energizing the radiation sources responsive to respective data bit input signals applied to the driver circuits during an information line period.
• One of the radiation sources is adapted to expose the photoreceptor with a plurality of relatively small pixels for reproduction of graphic information.
• the other radiation source is adapted to expose the photoreceptor with a plurality of relatively larger pixels for reproduction of text and drawing information.
• U.S. Patent 4,549,222 describes a single printer with controls therefor for printing at variable resolutions lower than the full capability of the printer.
• This patent does not address the problem of printing with an array of linear recording elements having an arrangement of N recording elements per square mm. , but requiring higher resolution recording than the usual N x N pixels per square mm. recording capability.
• increased resolution from non-impact printers using linear arrays of recording elements, such as LED's, have required closer packing of the recording elements. This substantially increases the cost of manufacturing printheads.
• One printer apparatus directed to this problem is described in U.K. patent publication 2,183,873; however, this apparatus requires that correction data also be furnished to the printhead for each line of recording. Such a printhead requires substantially higher data handling rates.
• One aspect of the invention is to provide improved printer apparatus for providing correction that does not require circuitry required for handling data at such high rates.
• an apparatus for reproducing images including line type information and pictorial information to be reproduced as a continuous tone or as a screen pattern comprising: a recording head having a plural number N of point-like recording elements per mm. extending so as to record along a line, the recording head emitting a line of dot recording emissions in response to data signals; an image receptor means having an area for recording emissions from the recording head on a line by line basis for reproducing the images; means for moving the image receptor means relative to the recording head; means for determining areas of the image representing pictorial areas to be reproduced; and characterized by control means providing data signals to the recording head for exposing M lines per mm.
• N x M dots per square mm. in the line type areas with a resolution of N x M dots per square mm. and providing data signals to the recording head for exposing L x M lines per mm. in the pictorial areas with a higher resolution of N x (L x M) dots per square mm. ; N, M and L being numbers greater than one and (L x M) being greater than N.
• the apparatus is* further realized by a recording head having a plurality of dot-like recording elements for recording on a recording member; means for moving the recording member relative to the recording head; means for activating particular recording elements in accordance with recording data related to the information to be printed to reproduce the data; means for compensating for the nonuniform output of some of the activated recording elements by further activating such some of the activated recording elements requiring compensation with additional activations that are provided at times both immediately before and after a respective data activation to provide for relatively symmetrical dot-like image elements wherein a compensation activation immediately before a data activation is of different duration than the one immediately after the data activation; and characterized by wherein the means for activating particular recording elements further includes a plurality of strobe lines, means connecting each recording element with only one of the strobe lines and means for providing different compensation signals on the strobe lines so that recording elements connected to one strobe line are compensated differently from recording elements connected to other strobe lines.
• FIG. 1 is an illustration of an original document sheet to be reproduced by the apparatus of the invention
• FIG. 2 is a schematic of a printing apparatus made in accordance with the invention.
• FIG. 3 is a block diagram of circuitry used in forming a printhead for use with the printing apparatus of FIG. 2;
• FIG. 4 is an illustration of a plurality of exposure points made with apparatus of the invention.
• FIG. 5 is a schematic of a second embodiment of printing apparatus made in accordance with the invention.
• FIG. 6 is a block diagram of circuitry used in forming a printhead for use with the printing apparatus of FIG. 5;
• FIG. 7 is a block diagram of a circuit interface for driving data to the printhead of FIG. 6;
• FIG. 8 is a block diagram of another embodiment of a circuit interface for driving data to the printhead of FIG. 6.
• a typical original document sheet D to be reproduced by the apparatus of the invention includes a continuous tone pictorial portion "P" that is surrounded by printed line type information "LT.”
• an electrophoto ⁇ graphic reproduction apparatus 10 includes a recording medium or photoreceptor such as a photoconductive web 12 or other photosensitive medium that is trained about four transport rollers 14, 16, 18 and 19, thereby forming an endless or continuous web.
• Roller 19 is coupled to a driver motor M in a conventional manner.
• Motor M is connected to a source of potential when a switch (not shown) is closed by a signal from logic and control unit (LCU) 31.
• LCU logic and control unit
• a charging station 30 is provided at which the photoconductive surface 15 of the web 12 is sensitized by applying to such surface a uniform electrostatic primary charge of a predetermined voltage.
• the output of the charger may be controlled by a grid connected to a programmable power supply (not shown).
• the supply is, in turn, controlled by the LCU 31 to adjust the voltage level Vo applied onto the surface 15 by the charger 30.
• an electrostatic image is formed by modulating the primary charge on an image area of the photoconductive surface with selective energization of point-like radiation sources in accordance with signals provided by a data source to be described.
• the point-like radiation sources are supported in a recording head or printhead 25 also to be described in more detail below.
• a development station 43 includes developer which may consist of iron carrier particles and electroscopic toner particles with an electrostatic charge opposite to that of the latent electrostatic image. Developer is brushed over the photoconductive surface of the web 12 and toner particles adhere to the latent electrostatic image to form a visible toner particle, transferable image.
• the development station may be of the magnetic brush type with one or two rollers. Alternatively, the toner particles may have a charge of the same polarity as that of the latent electrostatic image and develop the image in accordance with known reversal development techniques.
• the apparatus 10 also includes a transfer station 61 shown with a pair of corona chargers 62, 64 at which the toner image on web 12 is transferred in register to a copy sheet S; and a cleaning station 32, at which the photoconductive surface of the web 12 is cleaned of any residual toner particles remaining after the toner images have been transferred.
• a transfer station 61 shown with a pair of corona chargers 62, 64 at which the toner image on web 12 is transferred in register to a copy sheet S; and a cleaning station 32, at which the photoconductive surface of the web 12 is cleaned of any residual toner particles remaining after the toner images have been transferred.
• a transfer station 61 shown with a pair of corona chargers 62, 64 at which the toner image on web 12 is transferred in register to a copy sheet S
• a cleaning station 32 at which the photoconductive surface of the web 12 is cleaned of any residual toner particles remaining after the toner images have been transferred.
• the web has a plurality of indicia such as perforations along one of its edges. These perforations generally are spaced equidistantly along the edge of the web 12.
• suitable encoding means 24 for sensing web perforations. This sensing produces input signals into the LCU 31 which has a digital computer, preferably one or more microprocessors.
• the LCU has a stored program responsive to the input signals for sequentially actuating, then de-actuating, the work stations as well as for controlling the operation of many other machine functions.
• Additional encoding means 28 may be provided as known in the art for providing more precise timing signals for control of the various functions of the apparatus 10 as will be described below.
• microprocessors Programming of a number of commercially available microprocessors is a conventional skill well understood in the art. This disclosure is written to enable a programmer having ordinary skill in the art to produce an appropriate control program for the one or more microprocessors used in this apparatus. The particular details of any such program would, of course, depend on the architecture of the designated microprocessor(s).
• the printhead 25 is provided with a multiplicity of energizable point-like radiation sources 20, preferably light-emitting diodes (LED's).
• Optical means may be provided for focusing light from each of the LED's onto the photoconductive surface.
• the optical means preferably comprises an array of optical fibers such as sold under the name Sel oc, a trademark for a gradient index lens array sold by Nippon Sheet Glass, Limited. Due to the focusing power of the optical means, a row of emitters will be imaged on a respective transverse line on the recording medium.
• the printhead 25 comprises a suitable stationary support with a series of LED chip arrays mounted thereon.
• each of the LED chip arrays includes, for example, 128 LED's arranged in a single row. These chips are also arranged end-to-end in a row and where thirt -eight LED chip arrays are so arranged, the printhead will extend across the width of the web 12 and include 4864 LED's arranged in a single row. To each side of this row of LED's there may be provided, for example, thirty-eight identical driver chips. Each of these driver chips include circuitry for addressing the logic associated with each of 64 LED's to control whether or not each of the LED's should be energized as well as current driver circuitry 99 to control the level of current to each of the LED's controlled by that driver chip.
• Each of the two driver chips will be coupled for driving of alternate LED's, i.e., one of the driver chips will drive the even numbered LED's and the other driver chip will drive the odd numbered LED's in a particular LED chip array.
• one driver chip will drive the 64 odd numbered LED's of the 128 LED's in the array and the other driver chip will drive the 64 even numbered LED's of these 128 LED's. Only some of the even numbered LED's are illustrated in FIG. 3, it being understood that many more LED's are present.
• the original document sheet D forms a part of a multisheet document supported in a recirculating feeder tray 70.
• a vacuum drive roller under control of the LCU feeds the document D face down through metering rollers 72 which are adapted to feed the document D past an image scanning head 81 formed of say a conventional CCD array and provide signals to a conventional image scanner processor and buffer indicative of the movement of the sheet.
• a lamp 83 provides a narrow line of illumination, upon the document D and reflections thereof off the document D are sensed by the image scanning array to provide signals indicative of density information thereon.
• This output of the image scanner array is fed to the image scanner processor and buffer 75.
• the output of the data from the image scanner processor and buffer 75 is introduced into a continuous tone area detector 42 to identify the boundaries of the continuous tone information.
• the boundary defining the continuous tone picture can be inputted via a digitizing tablet or the image information and boundary data may be provided via a host computer, etc.
• the data representing the scanned image on document D along with data representing the boundaries of the continuous tone area P are fed over bus 44 to a raster image processor (RIP) 45.
• the RIP 45 processes this data and formats same in accordance with well known techniques and the output thereof is fed over to a page memory 46 wherein a page of rasterized data to be printed is stored.
• the output image between the boundaries of X. and X_ which contains the
• a B pictorial information will be processed to produce images at 400 x 800 addressable points per square inch of output information. In areas other than between X and X ⁇ , the output image is processed at 400 x 400 addressable points per square inch.
• the data information identifying the location of the pictorial information is stored in the LCU. This information may simply comprise the coordinates (see FIG. 1) X. and X_ referenced relative to a leading edge X Q of document D.
• the LCU In response to pulses from encoders 24 and 28 identifying a new image frame on a photosensitive web, the LCU provides an output signal to the Page Memory to remove one line of data.
• This data is fed to a conventional output device for formatting the data and synchronizing the operation thereof.
• This output device Is illustrated by the data driver and printer synchronizing device 56.
• This data indicated in FIG. 3 by lines D -D, is fed under clock control to an appropriate serial data shift register 22a, 22b, 22c and 22d (for the even numbered LED's) until 4864 bits of data, one for each of the LED's, is stored in the serial registers for the odd and even numbered LED's.
• the LCU Upon a signal from the LCU, the data (for the illustrated even numbered LED's) is shifted in parallel to latch registers 24a, 24b, 24c and 24d enabling the next line of data to be introduced into the serial shift registers.
• the LCU causes the output drivers logic device 47 to enable a trigger circuit providing a timed strobe signal.
• the output of the strobe is introduced to each of four logic OR gates 50-53.
• the output lines W, X, Y and Z of the logic OR gates are fed to one input of a logic AND gate 26 associated with each LED.
• the other input of AND gate 26 is provided with a data bit from the latch register representing whether or not a dot is to be printed at this time. Assuming a dot is to be printed, a respective LED is enabled for a time period predetermined by the strobe signal.
• four possible strobe signals may be selected from the following trigger devices: strobe device #1(48), strobe device #2(49), strobe device #3(54)and strobe device #4(55).
• Strobe #1 has a duration, in this example, of lOO ⁇ sec. and the strobe #2 a duration of 50 ⁇ sec.
• the strobe device #1 While reproducing the portion of the document between X and X , the strobe device #1 is used and is selected by logic device 47 in response to signals from the LCU. Adjacent LED's are spaced so as to provide 400 dots per inch (15.7 per mm). The encoder 28 provides pulses at the rate of 1/2400 per inch (0.01mm) of travel of the web 12. For exposing the text data in the areas between X to X and X ⁇ to X , it is sufficient that for line type of information that the exposure be made on the basis of 400 lines per inch (15.7 per mm) and that encoder pulses in between be effectively ignored. For this exposure, strobe #1 is employed and exposure pixels of two consecutive pixels (P..
• FIG. 4(b) For the line type and pictorial information between X A and X_, increased grey scale rendition is provided, particularly, to the pictorial information by exposing the photoconductor web on the basis of 800 lines per inch (31.5 per mm) in the in-track direction. To do this, the duration of each LED exposure in this area is reduced to 50 ⁇ sec. with the use of strobe #2(49) which is activated for each 1/800 inches (.032mm) of web movement. Note that the additional number of exposures to the pictorial area is accompanied with a corresponding reduction in exposure time for each pixel. In FIG.
• P 3 , P. and P ⁇ the pixels produced by three successive strobe signals are illustrated by P 3 , P. and P ⁇ .
• LED's are known to be nonuniform light emitters, it is highly desirable to ensure proper rendition that correction be provided to exposures, particularly, in the area reproducing the pictorial information.
• additional strobe devices #3(54) and #4(55) are provided.
• Strobe device #3 provides a strobe signal of lO ⁇ sec. duration while strobe device #4 provides a strobe signal of 5 ⁇ sec.
• strobes #3 and #4 both being used in addition to the nominal strobe value of 50 ⁇ sec
• each LED is tested to determine whether or not it needs correction in terms of requiring additional light output since similar LED's tend from LED to LED to emit variable amounts of light even though provided with identical driving currents.
• Those LED's requiring say 10% more "on-time” are attached to line Z which receives an input from strobe device #4.
• Those LED's requiring more "on-time” of say 20% are attached to line W which receives an input from strobe device #3.
• Those requiring more "on-time” of say 30% are attached to line X which receives an input from both strobe devices #3 and #4.
• An example of such additional exposure is shown schematically in FIG 4(a) with correction pixel P g representing a 10 ⁇ s exposure and correction pixel P ?
• a correction exposure of 5 ⁇ s (note the sizes of these are shown relatively larger to facilitate their viewing and that only one data pixel, P-, is shown with its correction pixels).
• Those LED's requiring no correction exposure are attached to line Y which receives an input from none of the strobe devices used for correction exposures, but only strobe signals of strobe devices #1 and #2.
• Lines W, X, Y, and Z also each receive strobe signals of strobe devices #1 and #2.
• the output drivers logic device 47 only switches on strobe device #1 (48) for each 1/400 of an inch (0.064 mm) of web drive where the printing of line type data corresponding to document areas X_ to X and X ⁇ to X tract (end of document) is to be made.
• the logic devices 47 switches to a null position where no strobe signal is provided at times t. , t ? , t.,, t. and t- until at t . the next pixel P is to be exposed
• the output drivers logic device 47 once again switches to strobe device #1 to trigger a strobe signal of 100 ⁇ s duration over lines W, X, Y and Z.
• the output drivers logic device 47 triggers strobe device #2 at each 1/800 inches (0.032 mm) of photoconductor web travel, i.e. say at times t_, t 3 and tg and at times t-,, t metro, t, and t 5 triggers strobe devices #3 and #4 used for correction.
• strobe device #3 is triggered at times t and t
• strobe device #4 is triggered at times t- and t f .
• the correction exposures are so overlapped with their associated image data exposure that no single low exposure isolated dot will exist on the printed page.
• Data signals D Q "D 3 must be output at a rate suitable for providing a new data bit at the AND gate 26 for each 1/800 of web travel (at least while operating on reproducing of areas between X to X ⁇ ); i.e., for strobe times t , t 3 and t g . But note that the availability of this extra data exposure period for pictorial reproduction is usable for increasing grey scale rendition on a printhead that is basically configured for bilevel reproduction of grey scale information.
• X ⁇ is also reproduced at 400 x 800 resolution to simplify the circuitry to the printhead.
• multiple strobe lines W, X, Y and Z are required with separate connection of each LED to a respective one of the four strobe lines. This adds some manufacturing cost to producing such a printhead.
• a compromise in cost versus quality may be made based on the assumption that the group of 64 odd numbered LED's in any LED array will have similar characteristics and will have current driven therethrough From a single driver chip that is adapted to drive all these 64 LED's. A similar statement may be made for the even numbered LED's in that array.
• an integrated circuit driver chip incorporating the serial registers, latch register and current driver for a group of LED's be connected to one of the strobe lines W, X, Y or Z based on say the average light output of the 64 LED's under control of that driver chip.
• all 64 LED's in that group will receive the appropriate same correction assuming, of course, that only those LED's that are activated to expose pictorial data receive such correction.
• FIGS. 5-7 a modified print apparatus is described wherein the same numerals refer to similar parts described for the apparatus embodiment in FIGS. 2-3.
• a still further simplification of printhead structure is achieved using a single strobe line ST.
• Operation of the apparatus 10' is similar to that described for the embodiment of FIGS. 2-3 except that the outputs of the strobe devices #3 and #4 and the strobe devices #1 and #2 are subject to a logic "OR" operation by "OR” device 100 to cause all strobe signals to be outputted on line ST.
• FIG. 7 a portion 56a of the data driver and printer synchronizing device 56' is shown.
• the rasterized print data for a line of dots to be printed is provided to one input of a solid state switch 104.
• a solid state switch 104 Since data for line portions 0 -D ⁇ are handled simultaneously, the devices described in FIG. 7 are actually multistage devices with single stages being illustrated for facilitating description thereof. In the example where all the data for the line is text or line-type data (data between
• the switch 104 transfers the data under a clock control into a shift register #1 (106). At an appropriate time, this data can then be shifted out to the printhead to appropriate shift registers 22a, 22b, 22c and 22d (FIG. 6) as well as to those registers (not shown) used to drive the odd numbered LED's for printing in accordance with the process described above at times t n , t g , etc
• the strobe signal on line ST for this is provided by strobe device #1 (48). For reproducing areas such as
• X through X ⁇ which include at least some pictorial information, the data D -D- for pixels or dot at times t_, t , t c , etc. is fed via
• a switch 120 operated under signal control by logic control 112 selects the output of the ROM being interrogated. For example, for obtaining the correction data for exposure times t.. , t,, etc., correction ROM 116 is interrogated and has its output ANDed with the data D O-D3. The resulting "data" is fed to switch 104 which is switched to select same under control of logic controller 112. The data is then clocked into shift register #1 (106) for subsequent shifting to the printhead as if it was actual data to be printed. The output from correction ROM #1 is selected to correspond to the
• ROM's are provided by a counter/decoder 114 which keeps count under pulse control of logic controller
• the counter/decoder uses the count as the address for fetching the correction data from the correction ROM's.
• U J o etc. with the correction data from correction ROM #1 determines the LED's which are to receive exposure of lO ⁇ s. Thus, only those LED's that are to be activated for the t n , t_, or t . , etc exposures are allowed to be enabled to be corrected during respective exposure periods t , t. , etc
• the original image data is also retained by, for example, having switch 110 connect the output of the shift register back into the input for storing same again.
• Other techniques and devices for retaining the data while outputting same are also contemplated.
• the same operation is repeated for the data in shift register #2 to subject same to the AND operation with the lower order correction bits from correction ROM #2 for obtaining correction "data" that is stored in shift register #1 (106) via switch 104.
• This correction "data” is sent to the printhead 25' and represents those LED's that were activated for a prior real data exposure such as at times t Q , t 3 , or t,, etc. and requiring a 5 ⁇ s correction exposure.
• the appropriate strobe signal ST will be selected by the LCU 31 and drive the output drivers logic 47 to select which one of the strobe signals to enable at the appropriate time. While separate trigger devices are shown to generate the different strobe signals, it will be appreciated that appropriate strobe signals may be provided by a single device that is say software controlled to output pulses of required duration.
• FIG. 8 may be used with the apparatus shown in FIGS. 5 and 6 in lieu of the interface shown In FIG. 7 to provide for more symmetrically shaped corrected pixels.
• the various parts or devices used in the FIG. 8 embodiment are similar with those shown in FIG. 7 and their numerical identification is provided with a (') to distinguish them from the devices or parts illustrated in FIG. 7.
• the data D -D Uber is fed by switch 104' to shift 0 3 register #1 (106') and then output through AND gate 122' to the printhead 25' (FIG. 6) via shift register
• Switch 120' which is the other input to
• AND gate 122' is switched to a source of logic high potential indicated by (+) to allow all data from register 106' to pass through the gate.
• the real data input on lines D -D. is fed by switch o 3
• the real data is also o recirculated back to register 106' via switch 104' for use in printing the data pixels P ' with strobe device #2 at time t .
• switch 120' switches to receive an input from its logic high (+) terminal to input this to one input of AND gate 122'.
• the real data is output from register 106' and input to the other input of AND gate 122'.
• the real data is thus output to shift register 108' and to the printhead for printing the data pixels P • using a strobe signal of 50 ⁇ s duration.
• the real data is also again recirculated back through switch 104' to register 106' for printing of the next set of correction pixels using correction ROM #2 (118').
• the real data is serially input into one input of AND gate 122' and "ANDed" with correction data from correction ROM #2 which is input through switch 120' to the second input of AND gate 122'.
• This correction data is then output through register 108' to the printhead registers 22a, 22b, 22c, and 22d, etc of printhead 25' (FIG. 6) for printing using strobe device #4 which has a pulse duration of
• a document having only text will be exposed on the basis of 400 x 400 dots per square inch (15.75 x 15.75 dots per square mm).
• a document is of mixed text and pictorial information required to be screened
• the portions of the text not determined to be in the area of the pictorial information are reproduced at 400 x 400 dots per square inch (15.75 x 15.75 dots per square mm)
• other portions of text and more importantly the pictorial information are exposed on the basis of 400 x 800 dots per square inch (15.75 x 3.1.5 dots per square mm) providing improved grey scale rendition.
• each of the correction pulses may be responsive to a separate encoder pulse.
• a series of pixels used in reproducing the pictorial portion and representing output of a single LED while the web moves in the direction "A" has nominal exposure pixels (P 3 , P., P 5 ) on a 400 x 800 per square inch (15.75 x 31.5 dots per square mm) basis with correction pixels (P c , P..) interspersed between o / the exposure pixels. While resolution herein is described in terms of the separate pixel exposures of each dot formed on the photoreceptor, it should be appreciated that in forming reproductions of the pictorial portion(s) requiring screening that clusters of such dots or pixels may be used to form larger dots or super pixels such as pixels of the so-called fattening type.
• the encorder means may be of the type described herein, wherein each line of printing is “tracked” relative to actual photoconductor movement or wherein an encoder signal is “tracked” at the beginning of each frame and pulses artificially created for each line in accordance with approximate photoconductor movement.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• General Engineering & Computer Science (AREA)
• Theoretical Computer Science (AREA)
• Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)

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• 1988
  • 1988-12-22 WO PCT/US1988/004593 patent/WO1989006464A1/en not_active Ceased
  • 1988-12-22 DE DE3853627T patent/DE3853627T2/de not_active Expired - Fee Related
  • 1988-12-22 EP EP89901203A patent/EP0349628B1/de not_active Expired - Lifetime

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